NASA's TESS space telescope has discovered a planetary system with three terrestrial planets that will allow us to study the characteristics of the atmosphere. NASA's Transiting Exoplanet Survey Satellite (TESS) has identified a planetary system composed of three planets with a mass similar to Earth, around a small nearby star, L 98-59, 35 light years away in the southern constellation of Volans. Among these, the smallest planet discovered so far by TESS, called L 98-59b, is between the sizes of Mars and Earth. This discovery is particularly important because it allows us to double the number of exoplanets (i.e. planets beyond our solar system) whose atmospheric characteristics can be studied with other telescopes, such as the future James Webb Space Telescope. The international team, led by Veselin Kostov, an astrophysicist at NASA's Goddard Space Flight Center and SETI, published the discovery in the June 27 issue of The Astronomical Journal. "The discovery is a great scientific result for TESS," says Giovanni Covone, an astrophysicist at the Department of Physics at Federico II University, a member of the international collaboration that uses the TESS space telescope to search for extrasolar planets around bright, nearby stars.
Luca Cacciapuoti, a Master's student in Physics with a passion for hunting extrasolar planets, contributed to the discovery. His bachelor's thesis was carried out within this collaboration, analyzing data from the first three months of TESS observations. "To study the atmospheres of Earth-like planets, we need to find systems with short-period orbits around bright stars," says Luca Cacciapuoti. "But such planets are difficult to detect. This new extrasolar system offers the possibility of fascinating future studies to which I hope to contribute again."
The three worlds have been discovered using the transit method, periodic decreases in the brightness of the star observed when a planet passes in front of it.
However, none of the planets lie within the "habitable zone", the range of distances from the star where liquid water could exist on the surfaces of the planets. All three receive much more energy from their star than Earth does from the Sun.
“The TESS mission seeks to answer questions fueled by our desire to understand where we come from and whether we are alone in the universe,” concludes Giovanni Covone. “If we were to observe the Sun from one of the worlds of the star L 98-59, transits via Earth and Venus might lead us to think that the planets are almost identical, but we know that they are not. We still have many questions about why Earth became habitable and Venus did not. If we can find and study similar examples around other stars, such as L 98-59, we could unlock some of these secrets.”
The discovery of the system around the L 98-59 star is based on data collected over three months of observation. The sky region of the 98-59 system will still be observed by TESS, allowing scientists to improve their knowledge of these planets and look for others in the same planetary system.
Planet L 98-59b is about 80% the size of Earth and is the smallest exoplanet discovered by TESS so far. Its host star, L 98-59, is a red dwarf about a third the mass of the Sun, located 35 light-years away. While L 98-59b is a record for TESS, even smaller planets have been discovered in data collected by NASA's Kepler satellite (operational until 2018), including Kepler-37b, which is only 20% larger than the Moon.
The other two worlds in the new planetary system, L 98-59c and L 98-59d, are 1,4 and 1,6 respectively times the size of the Earth.
"If there is more than one planet orbiting in a system, they could gravitationally interact with each other - said Veselin Kostov (NASA) - TESS will observe L 98-59 for a long enough period to be able to detect planets with orbits around 100 days. And if we're even a little lucky, we might even see the gravitational effects of undiscovered planets on the ones we currently know. "
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